1. Field of the Invention
This invention relates to microwave filters having at least one cavity with one or more end walls that are shaped to compensate for changes in temperature and to a method of construction thereof.
2. Description of the Prior Art
It is known to have temperature compensated filters. Previous filters have bimetal end caps that bend into a cavity of the filter with increases in temperature. The Collins, et al. U.S. Pat. No. 4,488,132 issued Dec. 11th, 1984 describes a resonant microwave cavity with a bimetal end cap or a trimetal end cap. In some previous filters, the end cap is made of two or more materials with different coefficients of thermal expansion, one of which is not metal. Even when one of the materials is not metal, the structure is referred to as being bimetal. The Atia, et al. U.S. Pat. No. 4,156,860 issued May 29th, 1979 describes a filter having a tuning plunger assembly where the assembly is formed by potting compounds such as a pourable silicon resin, which has properties of high thermal expansion. The Kick U.S. Pat. No. 4,677,403, issued Jun. 30th, 1987, describes a temperature compensated microwave resonator where a temperature compensating structure is bimetallic and there is a material having a higher temperature coefficient than the material forming the waveguide body that is affixed to the end wall by solder or by being bolted thereto. In addition, the temperature compensating structure includes means for varying the effective diameter of a tuning screw.
Bimetallic structures are much more expensive to manufacture than the end walls and irises of the present application. Further, whether the temperature compensating structure is a material having a high temperature coefficient that is bimetallic or is affixed to an end wall, it is extremely difficult to design the filter so that the temperature compensating structure works accurately. Further, bimetal end caps or irises have a much smaller temperature range over which they can successfully be made to operate when compared to the end caps and irises of the present invention.